Leak in 2nd floor toilet!

I installed a new toilet in the 2nd floor master bath on October 2011. About 3 weeks ago (June 2012), I noticed a leak coming through the ceiling on the 1st floor directly under the toilet.

My first thought was to replace the wax ring, so I tried that and the leak persisted. The toilet is up against a wall, and the drain pipe runs about 8 feet and drops down the opposite wall. When I turn the water off under at the water line below the tank, the leak stops. This means it can't be a leak in the line right? Otherwise it would still be leaking unless I shut the main off?

At this point should I start thinking about ripping up the tile and sub-floor?

At this point you should call a plumber and let him diagnose it BEFORE you go crazy and start tearing things apart. Unless water is leaking out of the tank, turning off the water should have NOTHING to do with stopping the leak, other than preventing you from flushing the toilet.

Leave the water on clean up floor and all porcelain meticulously. Now lay down newspaper on floor behind toilet and flush a lot. Newspaper shows a drop of water best. Toilets are not suppose to touch wall! My guess, the tank to toilet is leaking.
I two think You need a plumber.

Many installs require two wax rings. Unless the flange is above the finished flooring, you will need more then one wax ring.
Sometimes the flange is on the first floor, and then the secondary flooring is cut around the flange. It may be 5/8" underlayment or it may be backer board and tile. If that is the case, one wax ring wont do the job.